Field of the Invention
The present invention relates to a die cushion device and a control method of the die cushion device, and more particularly to a die cushion device and a control method of the die cushion device in which a cushion pad is moved up and down by using a hydraulic cylinder.
Description of the Related Art
Heretofore, this kind of die cushion devices are described in Japanese Patent Application Laid-Open No. 2006-142312 and Japanese Patent Application Laid-Open No. 2006-315074.
The die cushion device described in Patent Application Laid-Open No. 2006-142312 is a typical hydraulic servo die cushion device in which die cushion force is generated by using a proportion flow control valve (servo valve), and is composed of very simple components in a system using a servo valve.
In a die cushion process, in a state where an electromagnetic changeover valve is turned off (closed), hydraulic oil displaced from a hydraulic cylinder interlocking with a cushion pad pressed down by a slide is (limitedly) throttled by opening of from an A-port (a port communicating with a lower chamber of a hydraulic cylinder) to a T-port (a port communicating with a tank) of a servo valve so that die cushion pressure is generated in the hydraulic cylinder.
In a rising process, in a state where the electromagnetic changeover valve is turned on (opened), opening of from a P-port (a port communicating with an accumulator side) to the A-port, and of from a B-port (a port communicating with an upper chamber of the hydraulic cylinder) to the T-port, of the servo valve, is adjusted to cause the hydraulic cylinder to rise by using energy of pressure oil accumulated in the accumulator.
At that time, in a normal rising process, pressure oil at a relatively low pressure required for knocking out a product (and pressure oil having low energy) is accumulated in the accumulator.
In addition, in the die cushion device described in Japanese Patent Application Laid-Open No. 2006-315074, a discharge port of a hydraulic pump/motor is directly connected to a lower chamber of a hydraulic cylinder supporting a cushion pad, and torque control is performed for an electric motor connected to a rotating shaft of the hydraulic pump/motor on the basis of a die cushion pressure command and pressure in the lower chamber of the hydraulic cylinder to enable pressure in the lower chamber of the hydraulic cylinder (die cushion pressure) to be arbitrarily controlled.